Various types of debris or other undesirable materials are produced during the drilling, completion, production, intervention, and workovers of drilled wells. These materials, if not adequately managed, can cause various issues, spanning from decreasing the efficiency of well operations to complete loss of a well.
When debris is pumped or introduced to a drilling rig circulation system, such debris or trash has the potential to become lodged in downhole equipment utilized during drilling, intervention, workover, or completion causing sub-satisfactory performance or failure. In addition, downhole production equipment may also be impaired or restricted to future access.
Examples of debris or trash include, but are not limited to tools, paint chips, personal safety equipment, pipe dope, metal shavings, rust, fibers, precipitated fluid chemicals, mud, or formations. Any of the previously mentioned examples of debris have the potential to reduce performance or failure in surface or downhole equipment.
Traditional circulation filtration systems filter at low pressure, are comprised of settling tanks and pumps, or utilized a filtration medium such as diatomaceous earth or absolute filtration layers to remove undesirables from fluid systems. Most of these circulation systems focus on the cleanliness of fluid as it exits a well, only permits flow in one direction, requires manning by third party personnel, and negates contamination points between its discharge and well entry points.
Additionally, drilled wells that penetrate soft rock formations, typically located in offshore environments, often produce formation sand resulting in significant damage to wellbore equipment, surface facilities, and infrastructure utilized to transport hydrocarbon to commercial terminals. Well known industry sand control methods such as gravel packing or hydraulic fracturing are utilized to immobilize the formation sand and increase the productivity of wells. The methods utilize a combination of sand control screens and sand control tools to place uniquely sized proppant based on formation particle sized distribution to act as a filter and achieve the immobilization.
The operation of placing the uniquely sized proppant successfully relies on a sand control service tool being in the correct position, the integrity of a crossover port surviving the operation, and the integrity of sand control screens surviving deployment and the proppant placement operation.
Although methods to correctly identify tool placement and maintaining the desired placement throughout pumping operations has been battled and advances have been made on shelf wells, the ability to maintain and verify tool position becomes increasingly more difficult due to the existence of smaller companies utilizing older technology and new exploration reaching increasing farther depths. The consequence of a tool being in the incorrect position, or being pumped out of position, is proppant reaching the annular space above the sand control packer between the casing and the workstring/service tool assembly.
The failure of crossover port integrity is often attributed to erosion created by the properties and volumes of proppant placed during an operation. Reaching into the hundreds of thousands of pounds of proppant and sometimes into the millions, this failure exposes the gundrill ports of the crossover tool and subsequently the washpipe or annular space above the sand control packer between the casing and the workstring/service tool assembly to proppant.
Typically resulting in sticking the sand control service tool, the above failures are potentially recovered from through various recovery operations but may result in the loss of the target zone. An integrity breach of sand control screens also results in proppant reaching the annular space above the sand control packer between the casing and the workstring/service tool assembly, however, it bears the added consequence of proppant sticking to the inner string conduit (often referred to as washpipe) across the sand control interval, complete loss of sand control integrity, increased sand production and costs associated with handling/disposal at the surface, and potential loss of the well. It is this mode of failure that has the potential to go unrealized until a well is brought into production.
Aside from eliminating the potential for sticking the sand control service tool, it would be significantly desirable to know if sand control screen integrity exists prior to running the production tubing or moving off of location with the rig.
In addition to debris in the form of sand and misplaced proppant, drilling fluid and other materials pumped into the well may pose a threat to operations under certain circumstances. Riser pipes are used to connect a well at the seabed to a rig. In some cases, such as with a compliant tower, the riser is utilized to connect the subsea wellhead or subsea tree to a platform. In deepwater, the cold seawater temperature can cause congealing of the drilling fluid, such as mud, or precipitation of brine within the riser pipe. The larger internal diameter of riser in relation to its pressure ratings and optimum pump rate abilities of the rig typically lead to an insufficient ability to achieve the turbulent flow and annular velocities required to clean, displace, and carry all of the existing debris, congealed fluid, etc. from the pipe. Consequently, it can take several staged treatments and multiple days, depending on seabed depth, to successfully clean and displace riser to a suitable fluid for operations to proceed.